UV light from the sun has a wavelength within a range of 240 to 400 nm. UV light is classified into three zones by the wavelength range. That is, they are UV light (UV-A) having a long wavelength of 320 to 400 nm which is referred to as a suntan wavelength, UV light (UV-B) having a wavelength of 280 to 320 nm which is referred to as a sunburn wavelength and UV light (UV-C) having a low wavelength of 240 to 280 nm which is absorbed in the ozone layer over the earth and scarcely reach the surface of the earth. Since a lot of organic compounds exposed to these radiations are decomposed or rendered unstable, UV light has hitherto been the factor which deteriorates the value of various commercial products.
UV light absorbers have been added to polymeric materials (e.g. plastic, rubber, etc.), heat-sensitive recording sheets and inks for heat transfer or liquid crystal display materials in order to provide light-resistant (weather-resistant) materials which have resistance to fading due to sunlight. Further, they have been used for cosmetics, paints, lens, filters, films, etc., in order to prevent inflammation of the human body as well as deterioration of products due to UV light.
As the UV light absorbers, for example, there have hitherto been known compounds such as salicylate, benzophenone, benzotriazole, cyanoacrylate, hydantoin derivative and hindered amine (photostabilizer) and the like.
Since most of them absorb UV light having a wavelength of 290 to 380 nm, they are transparent and have no substantial influence on transparency of plastics or colored products. However, they have an insufficient absorptivity to UV light having a wavelength within a range of 360 to 400 nm.